You can exit EmulationStation and then, from the command line, run
sudo umount /media/usb0
If your USB drive is mounted on another folder than /media/usb0, substitute /media/usb0 with the proper folder name.
It's apparently the best solution... what i have do:
F4 to exit from ES.
mount (to found corrent usb)
used sudo umount
copyed all my news roms from pc and now also the image snap and some gamelist.xml from my personal system
type exit from console to restart es and....
@baconbandage Run the following command - with the gamepad plugged in - and post the output
Try testing the gamepad with the jstest utility. Exit EmulationStation and run
You should get a listing with the gamepad's input types (buttons/joysticks/etc.) and you can press the buttons/D-Pad/move joysticks to see if they are registering. You can exit the test by pressing Ctrl+C.
See the Docs on how to transfer games/roms to your RetroPie installation.
The easiest method is via file shares, from a PC in the same network. USB should be used when you don't have a network connection and yes, you can keep what info/files you have on it, RetroPie only looks in the retropie folder on the USB.
@darkwriter shoot! I just saw this. I had the exact same problem with my sn30pro controllers. Start+B for USB. I wish I had been here yeasterday to post. The manual gives zero clues about this. Glad they work now.